Blackboard heater

Hot water heat pump

The household water heat pump (also called hot water heat pump) is a separate device that heats water for domestic use to the desired temperature level. These units are about the size of a fridge-freezer combination and are equipped with integrated storage.

The hot water heat pump is an air-heat pump, i.e. it extracts energy or, respectively, heat, from the ambient air and thus uses the existing heat in the room. A hot water heat pump not only makes for a cooler cellar, but also for dryer air in the installation room. The air that was drawn in is transferred to the heat exchanger. The temperature of the refrigerant circulating inside is lower than the air flowing past. This causes the refrigerant to heat up and the air cools down. The air, which is now cold, is then discharged to the outside again. Since the outside air is directly routed through the evaporator of the air-water heat pump, the outside air condenses and the condensing water is discharged through a condensation drain - this process therefore reduces the moisture in the existing air.

The hot water heat pump can naturally also be operated from out of doors by way of inlet and outlet air systems. However, its coefficient of performance will then decrease markedly in the cold season. Today's hot water heat pumps usually have a respective control with a priority function for hot water preparation as soon as self-generated power is available from the PV system. Through this function, the hot water heat pump indirectly contributes to the storage of self-generated power.

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Inverter

Solar modules only generate direct current with low voltage for which there are only few suitable consumers. When the energy generated in the PV system is fed into the public grid, the direct current generated by the solar cells must be converted by the inverter to alternating voltage.

The use of an inverter also makes sense for direct consumption, because household appliances are not generally designed to operate with 230 V at 50 Hz.

Inverters work more efficiently if they are installed in a cool environment. If an inverter and a hot water heat pump are installed in the same room, both devices benefit from the respective "waste product" of the other:

The waste heat generated by the inverted uses the hot water heat pump directly to produce the hot water.

The cooling of the environment by the hot water heat pump in turn causes the inverter to work more efficiently.

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Power stores

Power from renewable energy sources does not flow continuously, but only if the sun is shining or the wind is blowing. But what happens if, precisely at that point in time, less power is needed? The flow of energy and the demand for energy only rarely correspond. Power is generally thought to be difficult to store.

The purpose of power storage is obvious: They make solar power available precisely when it is needed.

The power generated in a photovoltaic system is first of all used for own use. But if more power is available than is needed, the surplus solar power flows to the storage battery and charges it. Only when the battery is fully charged does the unneeded solar power reach the grid. And if the stored solar power is not sufficient for own use, additional power is obtained from the energy provider.

Because of the clear advantages of lithium ion batteries compared to lead batteries, these are increasingly implemented and have also been considered as standard in the photovoltaic area in recent years.

Conversion losses occur during the storage process, i.e. part of the energy is converted to heat. However, if the energy storage is installed in the same room as the hot water heat pump, both devices benefit here from the waste product of the other.

The power storage makes it possible to self-consume a large part of the solar power, which substantially reduces the amount of power that needs to be obtained from the energy provider.

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Metre box

In single-family houses, the circuit distributor is usually integrated in the metre box. The entire electrical system of the building converges in the metre box. Many energy provider demand separate metres for electric heating systems and heat pumps. This makes it possible to run the electrical heating system on a special, cost-effective tariff.

Single-family houses with this forward-looking technology now have at least 3, but mostly 4 metres:

yield counter - this measures the PV system's energy yield.

feed-in counter - this measures how much power was able to be sold to the energy provider. The difference between 2 and 3 quantifies the direct consumption.

consumption counter - this measures the amount of power bought from the energy provider. Frequently the consumption metre has to be complemented by a heating current metre (4). This counter quantifies the amount procured, divided into 2 different tariff classes, the high and the low tariff.

There are also energy providers which offer a special single tariff for heat pump heating systems. Newer metre locations frequently combine all different counters in one digital appliance.

Future metre boxes will accommodate more devices than just power counters: smart metre gateway, control box, control elements for energy management systems and additional protective devices. A win/win situation is created by renting out the own battery storage to the grid operator by "temporarily parking" surplus energy.

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Photovoltaic system

Photovoltaic (PV) means that the radiation energy of the sun is directly converted into electrical energy by way of solar cells.

The generated electricity can either be used on site or be feed into grids. If the energy is fed into the public grid, the direct current generated by the solar cells must be converted to alternating current by an inverter.

The electricity supply of the PV systems is divided into 3 different intended uses by a consumption counter:

self-generated power that can be consumed directly,

self-generated power that can be stored temporarily until consumption

and self-generated power that is sold to the energy provider as surplus.

The direct self-consumption (i.e. 1) can be significantly increased by using a power storage. The additional power procured from the energy provider can be offset against the fed-in power (i.e. 3).

If used in Germany, the energy required to produce a photovoltaic system is paid off in two to five years, i.e. after this time the PV system has amortised.

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Cost comparison of common heating systems

By now there are many different heating systems available for new buildings. Aside from the well-known gas condensing technology other technologies have established themselves in the last few decades: pellet heating, air-water heat pump, direct heat pump and efficient infrared heating systems. In order to heat a modern house that is insulated according to KfW specifications to a pleasant, cosy temperature, all systems mentioned above are potentially suitable.

But how about the costs? Calculating the total cost situation comprising procurement costs and operating costs over the total useful life is very elaborate for the end consumer. Mostly, concrete numbers or empirical values are missing. We have done the work for you so that you can make a direct cost comparison of infrared heating with other systems.

The calculation is based on the example of a 120-square-metre house that complies with the KfW standard. All aforementioned prices have been determined and calculated with great diligence. Nevertheless, we cannot assume any liability for this calculation. The price for power (24 cent/kWh) and the price for gas (5 cent/kWh) were ascertained in November 2017. All prices stated are non-binding gross prices. No legal claim can be derived. The one-off costs for the infrared heating system are comprised of € 7,072.00 for the heater and € 1,056.00 for the control.

Annual costs - p.a.

Energy requirement (gas/electricity)

Operating costs (gas/electricity)

Operating power for ancillary units

Maintenance costs

Chimney sweep costs

Repair costs

1) Total of operating costs - p.a.

One-off investment costs

One-off household connection costs

Total of one-off costs

2) One-off costs spread over 20 years operating life - p.a.

Total of operating costs and the one-off costs spread over the operating life (1+2) - p.a.

Infrared heat

3,805 kWh

€ 913.20

€ 0.00

€ 0.00

€ 0.00

€ 80.00

€ 993.20

€ 8,128.00

€ 0.00

€ 8,128.00

€ 406.40

€ 1,399.60

Directheat pump

1,810 kWh

€ 434.40

€ 0.00

€ 200.00

€ 0.00

€ 98.00

€ 732.40

€ 22,066.00

€ 0.00

€ 22,066.00

€ 1,103.30

€ 1,835.70

Gas heating

8,860 kWh

€ 443.00

€ 70.00

€ 200.00

€ 60.00

€ 204.00

€ 977.00

€ 18,655.00

€ 2,500.00

€ 21,155.00

€ 1,057.75

€ 2,034.75

Air-water heat pump

2,254 kWh

€ 540.96

€ 50.00

€ 200.00

€ 0.00

€ 210.00

€ 1,000.96

€ 23,232.00

€ 0.00

€ 23,232.00

€ 1,161.60

€ 2,162.56

Pellet heating

2,133 kWh

€ 507.00

€ 40.00

€ 230.00

€ 120.00

€ 124.00

€ 1,021.00

€ 29,089.00

€ 0.00

€ 29,089.00

€ 1,454.45

€ 2,475.45

Conclusion: Modern properties with considerably lower energy requirements than 20 or 30 years ago are today best heated using infrared radiation heat – that is, with electricity. The investment costs of all other systems, which are higher in each case, give the inexpensive infrared heating system a price advantage from day one. There is no need for decades of amortisation – you will be saving from the start.

Infrared radiation heat wins the cost comparison even without a photovoltaic system. Nevertheless, it is worthwhile to install a PV system – only then will you be largely independent of future rising energy costs, which, by the way, affect all types of heating in the same way.